The present invention relates to an internal combustion engine of two or more cylinders, supercharged by means of turbo-compressor units and provided with a cylinder head having four valves per cylinder, in which each half of the combustion chamber, separated by an imaginary line along the longitudinal axis of the engine, contains an exhaust valve and an induction valve. The cylinder heads of engines having four valves per cylinder, with the so-called "roof shape" combustion chambers normally have an arrangement which provides, in each half of the combustion chamber, two exhaust valves for one half chamber and two induction valves in the other half chamber.
Because of this the engine has all the induction manifolds on one side and all the exhaust manifolds on the other.
An arrangement of this type permits a rational installation of only one turbo-compressor unit, whilst the current tendency, above all in racing engines, is to utilise at least two turbo-compressor units for the purpose of reducing the "response time" and the loss of power at low engine speeds to the minimum.
In fact it is not easy to house two turbo-compressor units on the same side of the engine since the ducts which convey compressed air from the compressors to the induction manifolds become long and bulky and moreover create significant problems of space and of heat dissipation on the side of the engine where the two turbines are located.